It is known in the art to provide an internal combustion engine having an inherent unbalance condition with an engine mounted balancer driven by the engine crankshaft and rotating in timed relation therewith to offset some or all of the engine unbalance condition. Conventionally the balancer may be driven through a gear or chain drive and may include a single balance shaft or multiple balance shafts. As used in the following specification and claims, the terms “balancer” and “engine balancer” refer to a complete balance system or specified components thereof, including balance shafts or weights and their drive mechanisms, such as chains, drive and driven sprockets, gears and associated or equivalent components. “Engine output shaft” refers to a crankshaft or other output shaft, “Rotary input member” and “rotary output member” refer to input and output sprockets, gears and other equivalent devices.
In particular balancer embodiments adaptable to engines having an inherent second order pitching couple or vertical shaking force, the balancer is provided with dual balance shafts mounted on opposite sides of the engine block and rotating in opposite directions at twice crankshaft speed. The balancer shafts are driven by a chain which is engaged by an output sprocket connected with the engine crankshaft and driving first and second input sprockets. The first input sprocket is mounted on the first balance shaft and the second input sprocket is mounted on the engine and connects with a drive gear which engages a driven gear on the second balance shaft for rotating the second shaft in a direction opposite that of the first balance shaft and the engine crankshaft. In this application, a so-called inverted tooth chain is utilized which produces a high frequency vibration or “chain whine”. The vibration is carried into the balance shafts and the associated engine block which transmits the chain whine noise as audible engine noise.
A means of interrupting or decoupling the transmission of the chain whine vibration or noise from the drive chain to the engine-mounted balance shafts was accordingly desired to minimize this cause of audible engine noise.